Multiple-Input Multiple-Output Radio Transceiver

ABSTRACT

Abstract of Disclosure 
     A MIMO radio transceiver to support processing of multiple signals for simultaneous transmission via corresponding ones of a plurality of antennas and to support receive processing of multiple signals detected by corresponding ones of the plurality of antennas. The radio transceiver provides, on a single semiconductor integrated circuit, a receiver circuit or path for each of a plurality of antennas and a transmit circuit or path for each of the plurality of antennas.  Each receiver circuit downconverts the RF signal detected by its associated antenna to a baseband signal.  Similarly, each transmit path upconverts a baseband signal to be transmitted by an assigned antenna.

Background of Invention

[0001] This application claims priority to the following U.S.Provisional Patent Applications (the entirety of each of which isincorporated herein by reference):

[0002] Application No. 60/374,531, filed April 22, 2002;

[0003] Application No. 60/376,722, filed April 29, 2002;

[0004] Application No. 60/319,336, filed June 21, 2002;

[0005] Application No. 60/319,360, filed June 27, 2002; and

[0006] Application No. 60/319,434, filed July 30, 2002.

[0007] The present invention relates to a multiple-input multiple-output(MIMO) radio transceiver.

[0008] A primary goal of wireless communication system design is to usethe available spectrum most efficiently. Examples of techniques toincrease spectral efficiency include coded modulation techniques such asturbo codes and trellis-coded modulation, and multiple access techniquessuch as code division multiple access (CDMA).

[0009] Yet another way to optimize spectral efficiency that has recentlybecome popular in the academic community is the use of MIMO radiosystems. MIMO radio communication techniques have been proposed for usein, for example, 3G mobile telephone systems. However, prior efforts toexploit the benefits of a MIMO system have failed because, among otherreasons, a cost-effective MIMO radio could not be developed.

Summary of Invention

[0010] A MIMO radio transceiver is provided to support processing ofmultiple signals for simultaneous transmission via corresponding ones ofa plurality of antennas and to support receive processing of multiplesignals detected by corresponding ones of the plurality of antennas. TheMIMO radio transceiver is one that is suitable for a highly integratedand low cost fabrication. In addition, the radio transceiver can performMIMO transmit and receive operation in a portion of an RF band, up tosubstantially the entire RF band. The multiple transmit and receivepaths are particularly useful to support joint maximal ratio combiningtechniques, also referred to herein as composite beamforming (CBF).

[0011] The radio transceiver provides, on a single semiconductorintegrated circuit, a receiver circuit or path for each of a pluralityof antennas and a transmit circuit or path for each of the plurality ofantennas. Each receive path downconverts the RF signal detected by itsassociated antenna to a baseband signal, using either adirect-conversion process or a super-heterodyne (multiple conversion)process. Similarly, each transmit circuit upconverts a baseband signalto be transmitted by an assigned antenna, using either a directup-conversion process or a multiple-stage conversion process.

[0012] The multiple receive and transmit paths are integrated onto thesame semiconductor integrated circuit. This provides significant costand space/area savings. One use of this type of radio transceiver is toreceive and transmit signals that, at baseband, are processed using theaforementioned CBF techniques (whereby weighted components of a signalare sent via each of a plurality of antennas and received at the otherdevice by one or more antennas) to enhance the link margin with anothercommunication device. In such an application, it is very important thateach of the receive processing paths and each of the transmit processingpaths be matched in terms of amplitude and phase response. Because themultiple receive and transmit paths are integrated into a singlesemiconductor die, the processing paths will inherently be better phaseand amplitude matched, and any effects resulting from semiconductorintegration will track among the processing paths. Moreover, anyoperational changes due to temperature variations will also better trackamong the processing paths because they are integrated into the samesemiconductor integrated circuit.

[0013] Low cost radio transceiver solutions are provided that, forexample, do not require intermediate frequency (IF) filters, have poweramplifiers integrated on the radio transceiver integrated circuit (IC),use one frequency synthesizer, and integrate various control switchesfor transmit/receive and band select operations.

[0014] The above and other advantages will become more apparent withreference to the following description taken in conjunction with theaccompanying drawings.

Brief Description of Drawings

[0015]FIG. 1 is a general block diagram of a radio transceiver havingmultiple processing paths for multiple-input multiple-output (MIMO).

[0016]FIG. 2 is a schematic diagram of a MIMO radio transceiver having asuper-heterodyne architecture.

[0017]FIG. 3 is a schematic diagram of a MIMO radio transceiver having avariable intermediate frequency architecture.

[0018]FIG. 4 is a schematic diagram of a MIMO radio transceiver having adirect-conversion architecture.

[0019]FIG. 5 is a schematic diagram of radio front-end section usefulwith a MIMO radio transceiver.

[0020]FIGs. 6-8 are schematic diagrams showing alternative radiofront-end sections used with a MIMO radio transceiver.

[0021]FIG. 9 is a schematic diagram of still another radio-front enduseful in connection with two radio transceiver ICs in a single deviceto provide 4 transmit and receive paths.

[0022]FIG. 10 is a schematic diagram of yet another radio front-endsection useful in connection with a single radio transceiver IC thatprovides 4 transmit and receive paths.

[0023]FIGs. 11 and 12 are diagrams showing how digital-to-analogconverters and analog-to-digital converters may be shared in connectionwith a MIMO radio transceiver.

[0024]FIGs. 13 and 14 are diagrams showing how filters in the radiotransceiver can be shared so as to reduce the area of an integratedcircuit.

Detailed Description

[0025]FIG. 1 shows a block diagram of a radio transceiver 10. The radiotransceiver 10 is suitable for processing radio frequency signalsdetected by at least two antennas. The foregoing description is directedto an embodiment with two antennas 12 and 14, and an associated transmitand receive path for each, but this same architecture can be generalizedto support in general N processing paths for N-antennas. This radiotransceiver architecture is useful to support the aforementioned CBFtechniques. CBF systems and methods are described in U.S. PatentApplication No. 10/164,728, filed June 19, 2002 entitled "System andMethod for Antenna Diversity Scheme Using Joint Maximal RatioCombining"; U.S. Patent Application No. 10/174,689, filed June 19, 2002,entitled "System and Method for Antenna Diversity Using Equal Gain JointMaximal Ratio Combining"; and U.S. Patent Application No. 10/064,482,filed July 18, 2002 entitled "System and Method for Joint Maximal RatioCombining Using Time-Domain Signal Processing." These co-pending andcommonly assigned patent applications all relate to optimizing thereceived SNR at one communication based on the transmit vector used atthe other communication device.

[0026] One advantage of the technology described in the aforementionedpatent application entitled "System and Method for Antenna DiversityUsing Equal Gain Joint Maximal Ratio Combining" is that the output powerrequired from each antenna path is reduced. Therefore, the size of thepower amplifiers can be reduced, which reduces the overall semiconductorchip area of the IC, and makes it easier to isolate other RF circuitryon the IC from the power amplifiers.

[0027] The radio transceiver 10 comprises a receiver and a transmitter.The receiver comprises receiver circuits 20 and 30. There is a receivercircuit or section 20 for antenna 12 and a receive circuit or section 30for antenna 14. Similarly, the transmitter comprises a transmit circuit40 for antenna 12 and a transmit circuit 60 for antenna 14. Eachreceiver circuit 20 and 30 includes a downconverter 24, a variablelowpass filter 26 and a sample-and-hold circuit 28. Each transmitcircuit 40 and 60 includes a sample-and-hold circuit 42, a low passfilter 44, an upconverter 46, a bandpass filter 48 and a power amplifier50. The downconverters 24 may involve circuits to perform single-stage(direct) conversion to baseband or two-stage conversion to anintermediate frequency, then to baseband. Likewise, the upconverters 46may upconvert directly to RF or to an intermediate frequency, then toRF. More specific embodiments are described hereinafter in conjunctionwith FIGs. 2-4. The lowpass filters 44 may be variable filters toaccommodate transmission of signals in a variable bandwidth, similar tothe variable bandwidth receiver operation.

[0028] A front-end section 90 couples the radio transceiver 10 toantennas 12 and 14. There are switches 62 and 64 coupled to antennas 12and 14, respectively. Switch 62 selects whether the output of thetransmit circuit 60 or the input to the receiver circuit 20 is coupledto antenna 12. Switch 64 selects whether the output of the transmitcircuit 40 or the input of the receiver path 30 is coupled to antenna14. There are bandpass filters 22 coupled to one switch terminal of theswitches 62 and 64, respectively. In addition, there are lowpass filters52 and 54 coupled between the output of the power amplifiers 50 in eachtransmit circuit 40 and 60, and, the other switch terminal of theswitches 62 and 64, associated with antennas 12 and 14, respectively.

[0029] The outputs of the sample-and-hold circuits 28 of receivercircuits 20 and 30 are coupled to analog-to-digital converters (ADCs) 70and 72, respectively. The inputs to the sample-and-hold circuits 42 inthe transmit circuits 40 and 60 are coupled to digital-to-analogconverters (DACs) 80 and 82, respectively. The DACs 80 and 82 mayreceive as input first and second digital baseband transmit signalsrepresenting complex-weighted transmit signal components of a singlebaseband signal to be transmitted simultaneously from antennas 12 and14. The first and second transmitter circuits 40 and 60 process thefirst and second analog baseband signals for transmission substantiallysimultaneously. Likewise, antennas 12 and 14 may detect first and secondreceive signals, respectively, which are components of a single signalthat was transmitted to transceiver 10. The first receiver circuit 20and the second receiver circuit 30 process the first and second receivesignals substantially simultaneously to allow for a weighted combiningof the resulting digital baseband receive signals.

[0030] An interface and control block 92 is provided that interfaces theradio transceiver 10 with other components, such as a basebandprocessing section. For example, the interface and control block 92receives a filter bandwidth control signal, a center frequency controlsignal, and switch control signals, all of which are used to controloperation of certain components in the radio transceiver. Alternatively,the aforementioned signals may be sourced for a control processor orbaseband section and coupled directly to pins that are tied to theappropriate components of the transceiver 10.

[0031] The center frequency control signal controls the center frequencyof the local oscillator signals (not shown) used by the downconverters24 in each receiver circuit 20 and 30 and of the upconverters 46 in eachtransmit circuit 40 and 60. In addition, the filter bandwidth controlsignal controls the cut-off frequency of the variable lowpass filters 26(and optionally the lowpass filters 44 as well) for receiving signals ortransmitting signals of different bandwidths. The switch control signalscontrol the position of the switches 62 and 64 depending on whether thetransceiver 100 is receiving or transmitting.

[0032] One distinctive function of the radio transceiver 10 is tosimultaneously receive and process signals detected by each antenna 12and 14, in order to output first and second baseband receive signalsthat are combined appropriately using the aforementioned CBF techniques(in a baseband processor) to obtain a received signal. Conversely, theradio transceiver 10 simultaneously processes first and second basebandanalog transmit signals (representing weighted components of a singletransmit signal) and outputs them for transmission via antennas 12 and14, respectively. The radio transceiver 10 shown in FIG. 1 can beoperated in a half-duplex mode or, if desired, a full-duplex mode.

[0033] Moreover, the radio transceiver 10 may perform MIMO operation ina variable bandwidth. For example, the radio transceiver 10 may transmitor receive a signal in a single RF channel in a radio frequency band,such as a 20 MHz 802.11 channel of the 2.4 GHz band. However, it mayalso perform MIMO operation to transmit or receive a signal in a widerbandwidth, such as a higher data rate signal or signals that occupy upto substantially an entire frequency band, such as 80 MHz of the 2.4 GHzband. The filter bandwidth control signal sets the cut-off frequency ofthe lowpass filters 26 in each receiver circuit 20 and 30 to lowpassfilter the desired portion of RF bandwidth. The radio transceiver 10also has a receive-only non-MIMO operation where the output of eitherreceive path can be taken to sample any part or the entire RF band, byadjusting the lowpass filters 26 accordingly. This latter functionalityis useful to obtain a sample of a RF band to perform spectrum analysisof the RF band. As is explained in further detail in connection withFIGs. 13 and 14, the lowpass filters 44 in the transmitter may beeliminated and the variable lowpass filters 28 used for both receivedsignals and transmit signals.

[0034] The large dotted box around the receiver circuits 20 and 30 andthe transmit circuits 40 and 60 is meant to indicate that all of thesecomponents, including the power amplifiers 50, may be implemented on asingle semiconductor integrated circuit (IC). Other components may alsobe implemented on the IC as semiconductor and filter design technologyallows. The performance advantages achieved by integrating multipletransmit paths and multiple receive paths on the same semiconductor aredescribed above.

[0035]FIGs. 2-4 show more specific examples of the MIMO radiotransceiver shown in FIG. 1. FIG. 2 shows a dual-band radio transceiveremploying a super-heterodyne (two-stage) conversion architecture. FIG. 3shows a dual-band radio transceiver employing a walking intermediatefrequency (IF) conversion architecture using only one frequencysynthesizer. FIG. 4 shows a dual-band radio transceiver employing adirect conversion (single-stage) architecture. FIG. 5 illustrates aradio-front end section that can be used with any of the radiotransceivers shown in FIGs. 2-4.

[0036] With reference to FIG. 2 in conjunction with FIG. 5, radiotransceiver 100 will be described. The radio transceiver 100 shown inFIG. 2 is a super-heterodyne receiver that is capable of operating intwo different frequency bands, such as, for example, the 2.4 GHzunlicensed band and one of the 5 GHz unlicensed bands.

[0037] As shown in FIG. 5, the radio transceiver 100 is designed to becoupled to first and second antennas 102 and 104 via a RF front endsection 105 that includes transmit/receive (T/R) switches 106 and 108,which couple to antennas 102 and 104, respectively. Each T/R switch 106and 108 has an antenna terminal to be coupled to its associated antenna,a receive output terminal and a transmit input terminal and isresponsive to T/R switch control signals to select either the receiveoutput terminal or the transmit input terminal, depending on whether theradio transceiver is transmitting or receiving. Also in the RF front endsection 105 are band select switches 110, 112, 114 and 116 that selectthe output of the antenna from switches 106 and 108 depending in whichfrequency band a signal is being transmitted or received. Band selectswitches 110 and 112 are receive band select switches, each of which hasan input terminal coupled to the receive output terminals of the firstand second T/R switches 106 and 108, respectively, and a first outputterminal coupled to the BPFs 120 and 124 respectively, and a secondoutput terminal coupled to the BPFs 122 and 126 respectively. Bandselect switches 114 and 116 are transmit band select switches and eachhas first and second input terminals and an output terminal. The firstinput terminals of band select switches 114 and 116 are connected toLPFs 128 and 132, respectively, and the second input terminals ofswitches 115 and 116 are connected to LPFs 130 and 134, respectively.The output terminals of switches 114 and 116 are coupled to the transmitinput terminals of the first and second T/R switches 106 and 108,respectively.

[0038] Referring back to FIG. 2, on the receive side of the radiotransceiver 100, there is a receiver comprising a receiver path orcircuit 140 associated with signals detected by antenna 102 and areceiver path or circuit 170 associated with signals detected by antenna104. On the transmit side, there is a transmitter comprising a transmitpath or circuit 210 associated with antenna 102 and a transmit path orcircuit 230 associated with antenna 104. Each of the receiver circuits140 and 170 has two branches: a first branch to process a signal from afirst radio frequency band, and a second branch to process a signal froma second radio frequency band.

[0039] More specifically, each branch in the receiver circuits 140 and170 is coupled to a corresponding one of the bandpass filters 120, 122,124 or 126 in the RF front end section 105 shown in FIG. 5. In a firstbranch of the receiver circuit 140, there is a low noise amplifier (LNA)142 and an RF mixer 144 to downconvert an RF signal from a first radiofrequency band (RFB1) to an intermediate frequency (IF). In a secondbranch of the receiver circuit 140 there is an LNA 152 and an RF mixer154 that downconverts an RF signal from a second radio frequency band toIF. An IF filter (IFF) 145 is coupled to the mixer 144 and to the mixer154, and on the output side of the IFF 145 is a variable amplifier 146,quad mixers 148 and 156 and a variable lowpass filters 150 and 158. Asample-and-hold circuit 160 is coupled to variable lowpass filter 150and a sample-and-hold circuit 162 is coupled to variable lowpass filter158. As will be described in more detail hereinafter, the first branchof receiver circuit 140 (consisting of LNA 142 and mixer 144) processesa signal from a first RF band (RFB1) detected by antenna 102. The secondbranch of receiver circuit 140 (consisting of amplifier 152 and mixer154) processes a signal from a second RF band (RFB2) detected by antenna102. Only one of the branches of receiver circuit 140 is operating atany given time. As a result, the IFF 145 and the variable poweramplifier 146 can be shared by the branches (without the need for anadditional switch) assuming the output impedance of the mixers 144 and154 is high. The quad mixers 148 and 156 generate an in-phase signal (I)and a quadrature-phase (Q) signal of the signal supplied to the input ofthe variable amplifier 146. Thus, to summarize, the receiver circuit 140has a first downconverter consisting of an RF mixer (144 or 154,depending on what band branch is being used) that down-mix a firstreceive signal detected by antenna 102 (FIG. 5) to an intermediatefrequency signal, and quad mixers 148 and 156 that further down-mix theintermediate frequency signal to I and Q baseband analog signals.

[0040] The receiver circuit 170 has components 172 through 192 thatmirror those in the receiver circuit 140, but are used to process asignal from antenna 104 (FIG. 5) in either the first RF band (RFB1) orthe second RF band (RFB2). Like receiver circuit 140, receiver circuit170 has a second downconverter consisting of an RF mixer (174 or 184,depending on what band branch is being used) that down-mixes a secondreceive signal detected by antenna 104 to a second intermediatefrequency signal at the same IF as the first intermediate frequencysignal produced in receiver circuit 140, and quad mixers 178 and 186that further down-mix the second IF signal to I and Q baseband analogsignals.

[0041] Switches 200 and 202 are coupled to the sample-and-hold circuitsin receiver circuits 140 and 170, respectively, to switch between the Iand Q outputs associated with the first and second analog basebandreceive signals output by receiver circuit 140 and receiver circuit 170,respectively, for processing by an ADC. In addition, switches 270 and280 serve the additional function on the transmit side to receive asinput the output of DACs that supply first and second analog basebandsignals to be transmitted.

[0042] On the transmit side of the radio transceiver 100 there are twotransmit circuits 210 and 230. In transmit circuit 210, there are quadmixers 212 and 214 coupled to receive as input the I and Q data signals,respectively, that up-mix these signals by an intermediate frequencylocal oscillator signal to an IF. The outputs of the quad mixers 212 and214 are summed and coupled to the variable amplifier 216, which in turnis coupled to an RF mixer 218. The RF mixer 218 upconverts theintermediate frequency signal to RF, in either RFB1 or RFB2. Bandpassfilters 222 and 224 are coupled to the output of the mixer 218. Bandpassfilter 222 is associated with RFB1 and bandpass filter 224 is associatedwith RFB2. There is a power amplifier 226 coupled to the output of thebandpass filter 222 and a power amplifier 228 coupled to the output ofbandpass filter 228. The output of power amplifier 226 is coupled to theinput of the lowpass filter 128 (FIG. 5) and the output of poweramplifier 228 is coupled to the input of the lowpass filter 130 (FIG.5). To summarize, the first transmit circuit 210 has an upconverterconsisting of the quad mixers 212 and 214 that up-mix the baseband I andQ signals representing the first transmit signal, and the RF mixer 218that further up-mixes the intermediate frequency signal to produce afirst RF signal that is to be coupled to the first antenna 102 (FIG. 5).The output of the RF mixer 218 is coupled to bandpass branchesconsisting of BPF 222 and power amplifier 226 or BPF 224 and poweramplifier 228.

[0043] The transmit circuit 230 associated with antenna 104 hascomponents 232 through 248 and mirrors transmit circuit 210 to process asecond transmit signal component. Similar to the first transmit circuit210, the second transmit circuit 230 has an upconverter consisting ofquad mixers 232 and 234 that up-mix I and Q baseband signalsrepresenting the second transmit signal, and an RF mixer 238 thatfurther-up mixes the intermediate frequency signal to produce a secondRF signal that is coupled to the second antenna 104 (FIG. 5) fortransmission substantially simultaneous with the first RF signal.

[0044] The input signals to the transmitter circuits 210 and 230 aresupplied from DACs (not shown) to switches 270 and 280 that alternatelyselect between baseband I and Q signals, which are coupled to respectivesample-and-hold circuits 272 and 274 (in transmitter circuit 210) andsample-and-hold circuits 282 and 284 in transmitter circuit 230.Sample-and-hold circuits 272 and 274 are in turn coupled to LPFs 276 and278, respectively, and sample-and-hold circuits 282 and 284 are coupledto LPFs 286 and 288, respectively. LPFs 276 and 278 filter the basebandI and Q signals of the first transmit signal and supply their output tothe quad mixers 212 and 214, respectively. Likewise, the LPFs 282 and288 filter the baseband I and Q signals of the second transmit signaland supply their output to the quad mixers 232 and 234, respectively.The number of LPFs may be reduced if the variable LPFs in the receiverare used for both receive processing and transmit processing. Onetechnique for sharing the variable LPFs for transmit and receiveoperation is shown in FIGs. 13 and 14.

[0045] Since radio transceiver 100 is a super-heterodyne device, RFlocal oscillator signals for the radio frequencies associated with RFB1and RFB2 and IF local oscillator signals need to be generated. To thisend, there is an IF synthesizer (IF LO synth) 250 and a voltagecontrolled oscillator (VCO) 252 (including a 90ºphase component, notshown for simplicity) to generate in-phase and quadrature phase IF localoscillator signals that are coupled to the mixers 148, 156, 178 and 186,and to mixers 212, 214, 232 and 234. There is an RF local oscillatorsynthesizer (RF LO synth) 260 coupled to VCOs 262, 264 and 266 thatsupply different RF local oscillator signals to mixers 144, 154, 174 and184 on the receive side and to mixers 218 and 238 on the transmit side.There are multiple VCOs to supply RF signals for the multiple RF bands.For example, VCO 262 supplies an RF local oscillator signal (for any RFchannel in or the center frequency) for the 2.4 GHz unlicensed band, VCO264 supplies an RF local oscillator signal (for any RF channel in or thecenter frequency) for the low 5 GHz unlicensed band, and VCO 266supplies an RF local oscillator signal (for any RF channel in or thecenter frequency) for the high 5 GHz unlicensed band.

[0046] An interface and control block 290 interfaces a clock signal,data signals and an enable signal to/from an external device, such as abaseband processor and/or a control processor. Transceiver controlsignals sourced from an external device may be coupled to theappropriate transceiver components through the interface control block290 or coupled to pins that are tied to the appropriate components. Thetransceiver control signals include, for example, an RF center frequencycontrol signal, a filter bandwidth control signal, a transmit gainadjustment signal, a receive gain adjustment signal and switch controlsignals. The RF center frequency control signal controls which RF band,and the particular RF channel in that band, for which the RF LOsynthesizer 260 and associated VCOs 262, 264 or 267 outputs a localoscillator signal. An example of a frequency synthesizer suitable foruse with the radio transceivers described herein is disclosed incommonly assigned U.S. Provisional Application No. 60/319,518, filedSeptember 4, 2002, and entitled "Frequency Synthesizer for Multi-BandSuper-Heterodyne Transceiver Applications." The filter bandwidth controlsignal controls the cut-off frequencies of the variable lowpass filters150, 158, 180 and 188 in the receiver or the cut-off frequencies of thevariable lowpass filters 276, 278, 286 and 288 in the transmitter . Thetransmit gain control signals control the gain of the variableamplifiers 216 and 236 on the transmit side and the receive gain controlsignals control the gain of the variable amplifiers 146 and 176 on thereceive side. The switch control signals control the position of theswitches 106, 108, 110, 112, 114, 116, 200 and 202 according to theoperating mode of the radio transceiver 100 and the frequency band ofoperation.

[0047] The majority of the components of the radio transceiver 100 areimplemented in a semiconductor IC. The large dotted line indicates thosecomponents that may be included in the IC; however, additionalcomponents may be implemented in the IC.

[0048] With reference to FIGs. 2 and 5, operation of the transceiver 100will be described. For example, RFB1 is the 2.4 GHz unlicensed band andRFB2 is one of the 5 GHz unlicensed bands. It should be understood thatthe same architecture shown in FIG. 2 can be used for otherapplications, and that the 2.4/5 GHz dual band application is only anexample. For purposes of this example, the IF is 902.5 MHz, and thefrequency output by the IF LO synth 250 is 1805 MHz; the RF LOsynthesizer outputs an RF local oscillator signal that ranges from3319.5 MHz to 4277.5 MHz. The variable lowpass filters 150, 158, 180 and188 are controllable to filter a variety of bandwidths in the RF band,for example to facilitate MIMO receive processing of signals detected bythe antennas 102 and 104 in 20 MHz of bandwidth up to 80 MHz or 100 MHzof bandwidth. Similarly, the variable lowpass filters 276, 278, 286 and288 are controllable (by the filter bandwidth control signal) to filtera variety of bandwidths in the RF band, for example to facilitate MIMOtransmit processing of baseband signals to be transmitted in 20 MHz ofbandwidth up to 80 MHz or 100 MHz of bandwidth. Alternatively, and asdescribed hereinafter in conjunction with FIGs. 13 and 14, the variablelowpass filters 150, 158, 180 and 188 may be shared for receiveprocessing and transmit processing. Generally, the radio transceiver 100is operated in a half-duplex mode during which it does notsimultaneously transmit and receive in either RFB1 or RFB2.

[0049] The radio transceiver 100 may also be operated in a non-MIMOconfiguration. For example, the output of only one receive path may beused with the appropriate variable lowpass filter set to sample anyportion or all of the desired RF band for obtaining data to analyzingsome or all of the spectrum of that RF band.

[0050] The T/R switches and band select switches in the RF front-endsection 105 (FIG. 5) are controlled according to whether the radiotransceiver is transmitting or receiving, and in which RF band it isoperating.

[0051] For example, when the radio transceiver 100 is receiving in RFB1,switches 106 and 108 are moved to their top positions to select thereceive side of the transceiver 100. The RF LO synthesizer 260 iscontrolled to output RF local oscillator signals that will downconvert aparticular (sub-band) from RFB1. Switches 110 and 112 are moved to theirtop positions to select bandpass filters 120 and 124 (associated withRFB1) and corresponding branches of the receiver circuits 140 and 170.Filter 120 bandpass filters the signal detected by antenna 102 andfilter 124 bandpass filters the signal detected by antenna 104. Thelowpass filters 150, 158, 180 and 188 are controlled to operate in thedesired bandwidth. The two signals detected by antennas 102 and 104 maybe spatially diverse signal components of the same transmit signal. Thesignal from antenna 102 is downconverted to IF by mixer 144, filtered bythe IF filter 145, then downconverted to baseband I and Q signals byquad mixers 148 and 156 and filtered by lowpass filters 150 and 158.Each I and Q signal derived from this signal is sample-and-held andalternately selected for output to an ADC by switch 200. The receivercircuit 170 performs a similar operation for the signal detected byantenna 104.

[0052] The radio transceiver 100 performs MIMO transmit operation in asimilar manner. The LPFs 276, 278, 286 and 288 in the transmitter (orthe shared LPFs of the receiver) are controlled to filter the desiredbandwidth. In addition, the RF LO synth 260 is controlled to output anRF local oscillator signal according to which frequency band the signalsare to be transmitted. Assuming a signal is to be transmitted on achannel in RFB2, the switches 106 and 108 are moved to their bottompositions, selecting the transmit side of the radio transceiver 100. Theswitches 114 and 116 are moved to their bottom positions, selecting thebranch of transmit circuits 210 and 230 associated with RFB2. The analogbaseband signal to be transmitted consists of first and second signalcomponents, to be transmitted simultaneously by the respective antennas102 and 104. The appropriate RF local oscillator signal is output to themixers 218 and 238. The I and Q signals of a first transmit signalcomponent are upconverted to IF by quad mixers 212 and 214. The variableamplifier 216 adjusts the gain of the resulting IF signal, and the mixer218 upconverts the IF signal to RF. The filter 224 bandpass filters theRF signal output by the mixer 218 and the power amplifier 228 amplifiesthe output of the bandpass filter 224. Lowpass filter 130 filters theharmonics of the output of the power amplifier 228, and the resultingoutput is coupled to the antenna 102 via switches 114 and 106. A similaroperation occurs for the I and Q signals of the second transmit signalcomponent. The bandpass filter 246 filters the RF signal and the poweramplifier 248 amplifies the filtered signal, which is then coupled tothe lowpass filter 134. The resulting filtered signal is coupled toantenna 104 via switches 116 and 108.

[0053]FIG. 3 shows a radio transceiver 100' that is similar to radiotransceiver 100 except that it employs a variable or walking IFarchitecture, rather than a super-heterodyne architecture. Particularly,in the receiver circuits of the radio transceiver 100', the received RFsignal is down-mixed to an intermediate frequency that depends on the RFlocal oscillator signal, and an IF filter is not needed or is optional.A similar principle applies for the transmit circuits. Therefore, the RFlocal oscillator signal output of the RF LO synthesizer 260 is coupledto a divide-by-four circuit 265 which in turn supplies an IF localoscillator signal to mixers 148 and 156 in receiver circuit 140, mixers178 and 186 in receiver circuit 170, mixers 212 and 214 in the transmitcircuit 210 and mixers 232 and 234 in the transmit circuit 230. Thedivide-by-four circuit 265 generates the IF local oscillator signalbased on the RF local oscillator signal supplied by the RF LOsynthesizer 260. No IF filters are needed and only a single synthesizer(for the RF local oscillator signal) is required. Otherwise, theoperation of the radio transceiver 100' is similar to that of radiotransceiver 100.

[0054] The radio transceivers of FIGs. 2 and 3 have certain advantagesthat make them suitable for highly integrated and low costimplementations. First, the super-heterodyne architecture of FIG. 2 andthe walking IF architecture of FIG. 3 allow for integrating the poweramplifiers in the transmitter of the radio transceiver IC. This isbecause the power amplifier output frequency falls significantly outsidethe VCO turning range, thereby avoiding injection locking of the VCO.This is not as easily possible in other architectures, such as thedirect conversion architecture shown in FIG. 4. Second, the walking IFtransceiver of FIG. 3 does not require an IF filter which reduces thebill of materials cost of the radio transceiver. Even thesuper-heterodyne design of FIG. 2 can be implemented without an IFfilter under certain design parameters. The design of FIG. 3 has boththe advantage of more easily integrating the power amplifiers as well asnot requiring an IF filter. Therefore, the radio transceiver design ofFIG. 3 may be desirable where cost, integration and IC size areimportant.

[0055] Referring now to FIG. 4, a direct-conversion radio transceiverarchitecture 300 is described. Like radio transceiver 100, radiotransceiver 300 has multiple receiver circuits 310 and 340 in thereceiver and multiple transmit circuits 370 and 400 in the transmitter.The receiver circuits are identical and the transmit circuits areidentical. In the receiver circuit 310, there are two amplifiers 312 and314 both coupled to a switch 316. Amplifier 312 receives a bandpassfiltered signal in frequency band RFB1 from a bandpass filter in the RFfront end section 105 (FIG. 2), and similarly amplifier 314 receives abandpass filtered signal in frequency band RFB2. The output of theswitch 316 is coupled to a variable amplifier 318 to adjust the gain ofthe signal supplied to its input. The output of the variable amplifier318 is coupled to mixers 320 and 322 that down-mix the amplified receivesignal by IF local oscillator signals to produce I and Q signals. Theoutput of mixer 320 is coupled to a lowpass filter 324, and the outputof mixer 322 is coupled to a lowpass filter 326. The lowpass filters 324and 326 are, for example, third order lowpass filters that may belocated off-chip from the remainder of the transceiver components forbetter linearity. The outputs of lowpass filters 324 and 326 are coupledto variable lowpass filters 328 and 330, respectively. Variable lowpassfilters 328 and 330 can be controlled to vary their cut-off frequency soas to select either a narrowband (e.g., 10 MHz) or a wideband (e.g., 40MHz). The variable lowpass filters 328 and 330 are coupled tosample-and-hold circuits 332 and 334, respectively. The output of thesample-and-hold circuits 332 and 334 are baseband I and Q signalsrepresenting the signal detected by antenna 102. A switch 336 iscontrolled to alternately select between the baseband I and Q signalsfor coupling to a single ADC, saving the cost of a second ADC.

[0056] Receiver circuit 340 has components 342 through 366 which are thesame as the components in receiver circuit 310. Receiver circuits 310and 340 perform a direct-conversion or zero-intermediate frequencydownconversion of the detected RF signals to baseband. To summarize, thefirst receiver circuit 310 has a first downconverter comprising quadmixers 320 and 322 that down-mix a first receive signal detected byantenna 102 directly to baseband I and Q signals. Likewise, the secondreceiver circuit 340 has a second downconverter comprising quad mixers350 and 352 that down-mix a second receive signal detected by antenna104 directly to baseband I and Q signals.

[0057] It will be appreciated by those with ordinary skill in the artthat in the receiver circuits 310 and 340, quad mixers 320 and 322, andquad mixers 350 and 352 may be broadband mixers capable of covering bothRFB1 and RFB2, or alternatively separate quad mixers may be provided foreach RF band.

[0058] On the transmit side, transmit circuit 370 comprises first andsecond sample-and-hold circuits 372 and 374 that receive I and Qbaseband signals for a first transmit signal from switch 371. Theoutputs of the sample-and-hold circuits 372 and 374 are coupled to thevariable lowpass filters 376 and 378. The outputs of the lowpass filters376 and 378 are coupled to quad mixers 380 and 382, respectively. Thequad mixers 380 and 382 up-mix the filtered I and Q signals output bythe lowpass filters 376 and 378 to output RF I and Q signals which arecombined and coupled to a variable amplifier 384. The variable amplifier384 adjusts the gain of the first RF signal and supplies this signal tobandpass filters 386 and 388, associated with RFB1 and RFB2,respectively. The outputs of bandpass filters 386 and 388 are coupled topower amplifiers 394 and 396. Power amplifiers 390 and 392 amplify theRF signals for frequency bands RFB1 and RFB2 which are coupled to the RFfront end 105.

[0059] Transmit circuit 400 has components 402 through 422 that are thesame as those in transmit circuit 370. The input to transmit circuit 400consists of I and Q signals for a second transmit signal alternatelysupplied by switch 401. Thus, to summarize, the first transmit circuit370 comprises an upconverter consisting of quad mixers 380 and 382 thatdirectly up-mix baseband I and Q signals to RF I and Q signals that arecombined to form a first RF signal. The second transmit circuit 400comprises an upconverter consisting of quad mixers 410 and 412 thatdirectly up-mix baseband I and Q signals to RF I and Q signals that arecombined to form a second RF signal. The variable lowpass filters in thereceiver may be shared for transmit processing to remove the need forthe variable lowpass filters in the transmitter.

[0060] A dual modulus phase-lock loop (PLL) 430, VCOs 432, 434 and 436,a squaring block 438 and a 90ºphase shifter 440 may be provided tosupply the appropriate in-phase and quadrature RF local oscillatorsignals to the mixers 320 and 322, respectively, in receiver circuit310; mixers 350 and 352 in receiver circuit 370; mixers 380 and 382,respectively, in transmit circuit 370; and mixers 410 and 412,respectively, in transmit circuit 400. The dual modulus PLL 430 is astandard component for generating high frequency signals. The squaringblock 438 acts as a frequency doubler, reducing pull of the VCO by thepower amplifiers. For example, in order to provide RF mixing signals forthe 2.4 GHz unlicensed band and the high and low 5GHz unlicensed band,the VCO 432 produces an RF signal in the range 1200 through 1240 MHz,VCO 434 produces an RF signal in the range 2575 through 2675 MHz, andVCO 436 produces an RF signal in the range 2862 through 2912 MHz.

[0061] Like radio transceiver 100, there are control signals that arecoupled to the appropriate components to control the operation. Radiotransceiver 300 operates very similar to radio transceiver 100 or 100'.There are filter bandwidth control signals to control the variablelowpass filters in the receiver or transmitter depending on thebandwidth of operation of the transceiver 300. There are receive gaincontrol signals to control the variable amplifiers 318 and 348. Thereare switch control signals to control the various switches in the radiotransceiver 300 and front-end section, depending on whether it is in thereceive mode or transmit mode, and depending on which band, RFB1 orRFB2, the transceiver is operating in. There are RF center frequencycontrol signals to control the dual-modulus PLL 410 and VCOs 412-416depending on which RF band and RF channel in that band the transceiveris operating in. There are transmit gain control signals to control thevariable amplifiers 384 and 414 in the transmit circuits.

[0062] It should be understood that although the filter bandwidthcontrol signals shown in FIGs. 2-4 are shown only coupled to thereceiver circuits, these signals may also be coupled to the transmittercircuits to control the variable lowpass filters in the transmittercircuits, if the filter sharing techniques referred to herein are notemployed.

[0063]FIGs. 6-10 illustrate alternative front-end sections. In FIG. 6,the front-end 500 section comprises many of the same components asfront-end section 105, albeit in a slightly different configuration. TheLPFs 128, 130, 132 and 134 may be integrated on the radio transceiver ICor incorporated in the radio front-end 500. Instead of switches 106 and108, diplexers 502 and 504 are used for band selection from the antennas102 and 104. As known in the art, a diplexer is a 3-port device that hasone common port and two other ports, one for high frequency signals andone for lower frequency signals. Thus, the diplexers 106 and 108 serveas band select switches. In the example of FIG. 6, the two bands thatare supported are the 2.4 GHz band and the 5.25 GHz band. Switches 110,112, 114 and 116 are transmit/receive switches that select theappropriate signals depending on whether the radio transceiver istransmitting or receiving. For example, when the radio transceiver istransmitting a signal in the 2.4 GHz band through antennas 102 and 104,the diplexer 502 receives the first 2.4 GHz transmit signal from switch110 and couples it to the antenna 102, and the diplexer 504 receives thesecond 2.4 GHz transmit signal from switch 114 and couples it to antenna104. All the other switch positions are essentially irrelevant.Likewise, when receiving a signal in the 5.25 GHz band, diplexer 502couples the first 5.25 GHz receive signal from antenna 102 to switch 112and diplexer 504 couples the second 5.25 GHz receive signal from antenna104 to switch 116. Switch 112 selects the output of the diplexer 502 andswitch 116 selects the output of the diplexer 504.

[0064] As is known in the art, the radio transceiver is coupled to abaseband processor that may be a separate integrated circuit as shown bythe baseband integrated circuit (BBIC) 510 in FIGs. 6 and 7.

[0065]FIG. 7 illustrates a front-end section 500' that is similar tofront-end section 500 except that the transmit/receive switches areeffectively integrated on the radio transceiver IC. Many techniques areknown to integrate switches similar to the transmit/receive switches onthe radio transceiver IC. When the transmit/receive switches areintegrated on the radio transceiver IC, for each antenna, a quarter-waveelement 515 is provided in the radio front-end 500" at each band branchoff of the diplexer for each antenna. FIG. 8 shows this configurationfor one antenna 102 only as an example, but it is repeated for eachantenna. When a signal is being transmitted, the transmit/receive switchis switched to the terminal that is connected to ground so that thesignal output by the corresponding power amplifier (PA) of thetransmitter is selected and coupled to the diplexer, and when a signalis received, it is switched to the other terminal so that the receivesignal passes through the quarter-wave element 525, the transmit/receiveswitch and passes to the LNA in the receiver. The quarter-wave element515 may be any quarter-wave transmission line. One example of animplementation of the quarter-wave element 515 is a microstrip structuredisposed on a printed circuit board. The quarter-wavelengthcharacteristic of the quarter-wave element 515 creates a phase shiftthat acts as an impedance transformer, either shorting the connectionbetween the bandpass filter and ground, or creating an open circuit,depending on the position of the switch.

[0066] The radio transceiver IC and front-end configurations shown inFIGs. 6 and 7 are useful for network interface cards (NICs) to serve asan 802.11x WLAN station.

[0067]FIG. 9 illustrates a front-end section 600 that interfaces withtwo radio transceiver ICs to provide a 4 path MIMO radio transceiverdevice. One example of a use for this type of configuration is in anaccess point (AP) for a WLAN. Whereas the radio transceiverconfigurations described up to this point were for 2-path MIMOoperation, 4-path MIMO operation provides even greater link margin withother devices when used in connection with the maximal ratio combiningschemes referred to above.

[0068] The front-end section 600 interfaces two radio transceiver ICs toeight antennas 602 through 616. A BBIC 660 is coupled to the two radiotransceiver ICs that operate in tandem to transmit 4 weighted componentsof a single signal or to receive 4 components of a single receivedsignal. Antennas 602, 606, 610 and 614 are dedicated to one frequencyband, such as the 2.4 GHz band and antennas 604, 608, 612 and 616 arededicated to another frequency band, such as a 5 GHz band. In thefront-end section 600, there are transmit/receive switches eight 620through 634 each associated with one of the antennas 602 through 616respectively. There are also eight bandpass filters 640 through 654coupled to respective ones of the transmit/receive switches 620 through654. The transmit/receive switches 620 through 634 could be integratedon the respective radio transceiver ICs instead of being part of thefront-end section 600. Though not specifically shown, the LPFs are alsointegrated on the radio transceiver ICs. Operation of the front-endsection 600 is similar to what has been described above. Thetransmit/receive switches 620 through 654 are controlled to select theappropriate signals depending on whether the radio transceiver ICs areoperating in a transmit mode or a receive mode.

[0069]FIG. 10 illustrates a front-end section 600' that is similar tofront-end section 600 but excludes the transmit/receive switches.Moreover, the radio transceiver 670 is a single IC that integrates4-paths (what is otherwise included on two radio transceiver ICs asshown in FIG. 9). The transmit/receive switches are integrated on theradio transceiver IC 670. The operation of the front-end section 600' issimilar to that of front-end section 600. FIG. 10 illustrates theability to scale the number of MIMO paths to 3, 4 or more separatepaths.

[0070]FIGs. 9 and 10 also illustrate the radio transceivers 100, 100'and 300 deployed in multiple instances to support multiple channelcapability in a communication device, such as an AP. For example, asshown in FIG. 9, one radio transceiver, such as an access point, couldperform 2-path MIMO communication with devices on a channel while theother radio transceiver would perform 2-path MIMO communication withdevices on another channel. Instead of interfacing to one baseband IC,each would interface to a separate baseband IC or a single baseband ICcapable of dual channel simultaneous operation.

[0071]FIGs. 11 and 12 show a configuration whereby the number of DACsand ADCs that are coupled to the radio transceiver can be reduced.Normally, a separate DAC or ADC would be required for every signal thatrequires processing. However, in a half-duplex radio transceiver, sincetransmit and receive operations are not concurrent, there is opportunityfor sharing DACs and ADCs. For example, FIG. 11 shows a configurationcomprising two ADCs 710 and 720 and three DACs 730, 740 and 750. ADC 720and DAC 730 are shared. Switch 760 selects input to the ADC 720 andswitch 770 selects the output of the DAC 730. A digital multiplexer(MUX) 780 is coupled to the ADC 720 to route the output therefrom, andto the DAC 730 to coordinate input thereto. The ADCs, DACs and digitalMUX 780 may reside on a separate integrated circuit from the radiotransceiver integrated circuit. For example, these components may resideon the baseband integrated circuit where a baseband demodulator 790 anda baseband modulator 795 reside.

[0072] The number of ADCs is reduced by using a single ADC 720 todigitize both the received Q signal and the transmit power level signal.Similarly, the number of DACs is reduced by sharing a single DAC 730 toconvert both the transmit I signal and the receiver gain control signal.The digital MUX 780 selects the signal (either the transmit I signal orthe receiver gain control signal) that is supplied as input to theshared DAC 730. Similarly, the signal that is output by the shared ADC720 (digital received Q signal or the digital transmit power levelsignal) is routed to the appropriate destination by the digital MUX 780.

[0073] As described above, one way to facilitate sharing of the ADC andthe DAC is to provide switches 760 and 770. These switches may reside onthe radio transceiver IC. An output terminal of switch 760 is coupled tothe shared ADC 720, one input terminal is coupled to the LPF at theoutput of the local oscillator that generates the received Q signal andthe other input terminal is coupled to the output of the power detectorthat generates the transmit power level signal. Switch 760 is controlledto select one of two positions, depending on whether the ADC is to beused for the received Q signal or the transmit power level signal.Likewise, an input terminal of switch 770 is coupled to the shared DAC730, one output terminal is coupled to the variable power amplifier inthe receiver and the other output terminal is coupled to the LPF thatsupplies a transmit I signal to the in-phase local mixer in thetransmitter. Switch 770 is controlled to select one of two positions,depending on whether the shared DAC is to be used for the receiver gaincontrol signal or the transmit I signal. The configuration shown in FIG.11 can be repeated for each receive path/transmit path pair in thetransceiver.

[0074] It should be understood that the switches 760 and 770 areoptional. As shown in FIG. 12, they may be replaced with common signalpaths if the radio transceiver IC is a half-duplex transceiver, meaningthat the receiver and transmitter are not operational at the same time.Therefore, the shared DAC 730, for example, will convert whicheverdigital signal is supplied to it (the transmit I signal or the receivergain control signal, depending on whether the transceiver is in receivemode or transmit mode), and the DAC 730 will output the analog versionof that signal on both paths. If the transmit I signal is selected forprocessing by the shared DAC 730, the receiver will be off, so couplinga analog version of the transmit I signal to the variable poweramplifier in the receive channel will have no effect, but it also willbe coupled to the in-phase local oscillator in the transmitter, which isdesired. A similar situation holds true if the switch for the shared ADC720 is replaced with a common signal path configuration.

[0075] A single ADC and a single DAC can be shared among signals fromthe transmitter and receiver (since in a half-duplex transceiver, thetransmitter and receiver are generally not operational at the sametime). The signals that are identified above are only examples of thetransmitter and receiver signals that may be multiplexed to a single ADCor single DAC.

[0076]FIGs. 13 and 14 illustrate configurations that allow for sharingof the LPFs used to filter the baseband receive signals and basebandtransmit signals in the radio transceivers of FIGs. 2-4. As an example,a single antenna path of the direct conversion radio transceiver 300 isselected to illustrate the filter sharing technique. Some intermediatecomponents, such as variable amplifiers and sample-and-hold circuits,are not shown for simplicity. LPFs 328 and 330 are shared to both filterthe received I and Q signals (RX I and RX Q) associated with an antenna,such as antenna 102, and filter the baseband transmit I and Q signals(TX I and TX Q) to be transmitted. The switches 710 and 720 each havetwo input terminals and an output terminal coupled to the input of theLPFs 328 and 330, respectively. Coupled to the input terminals of theswitch 710 are the receive I signal output by the quad mixer 320 and thebaseband transmit I signal. Similarly, coupled to the input terminals ofthe switch 720 are the receive Q signal output by the quad mixer 322 andthe baseband transmit Q signal. A transmit/receive control signal iscoupled to the switches 710 and 720 to cause the switches to selecteither their terminals to which the receive I and Q signals areconnected or the terminals to which the transmit I and Q signals areconnected. In FIG. 13, it is assumed that the output impedance at eachfilter is low and each load impedance is high (typical in most analogICs) so that the output of each filter can be summed. Therefore, only asingle multiplexer is needed at the input to the filters. Theconfiguration of FIG. 14 is similar to FIG. 15, except that additionalswitches 730 and 740 are provided in case the impedances are not asdescribed above.

[0077] In sum, a multiple-input multiple-output (MIMO) radio transceiveris provided comprising a receiver and a transmitter. The receivercomprises at least first and second receiver circuits each to process asignal from a corresponding one of first and second antennas. The firstreceiver circuit comprises a first downconverter coupled to the firstantenna to downconvert a first receive signal detected by the firstantenna to produce a first baseband signal; and a first lowpass filtercoupled to the first downconverter that lowpass filters the firstbaseband signal. The second receiver circuit comprises a seconddownconverter coupled to the second antenna to downconvert a secondreceive signal detected by the second antenna to produce a secondbaseband signal; and a second lowpass filter coupled to the seconddownconverter that lowpass filters the second baseband signal. Thetransmitter comprises at least first and second transmitter circuitseach of which processes a signal to be transmitted by a correspondingone of the first and second antennas. The first transmitter circuitcomprising a first upconverter that upconverts a first baseband analogsignal to generate a first RF frequency signal; a first bandpass filtercoupled to the output of the first upconverter that filters the first RFfrequency signal; and a first power amplifier coupled to the output ofthe bandpass filter that amplifies the filtered RF frequency signal toproduce a first amplified signal that is coupled to the first antennafor transmission. Similarly, the second transmitter circuit comprises asecond upconverter that upconverts a second baseband analog signal togenerate a second RF frequency signal; a second bandpass filter coupledto the output of the second upconverter that filters the second RFfrequency signal; and a second power amplifier coupled to the output ofthe second bandpass filter that amplifies the second filtered RFfrequency signal to produce a second amplified signal that is coupled tothe second antenna for transmission.

[0078] Similarly, a multiple-input multiple-output (MIMO) radiotransceiver is provided comprising a receiver comprising at least firstand second receiver circuits each to process a signal from acorresponding one of first and second antennas, and a transmitter. Thefirst receiver circuit comprises a first downconverter coupled to thefirst antenna to downconvert a first receive signal detected by thefirst antenna to produce a first in-phase baseband signal and a firstquadrature-phase baseband signal; and first and second lowpass filterscoupled to the first downconverter that lowpass filter the firstin-phase baseband signal and the first quadrature phase baseband signal,respectively. The second receiver circuit comprises a seconddownconverter coupled to the second antenna to downconvert a secondreceive signal detected by the second antenna to produce a secondin-phase baseband signal and a second quadrature-phase baseband signal;and third and fourth lowpass filters coupled to the second downconverterthat lowpass filter the second in-phase baseband signal and the secondquadrature-phase baseband signal. The transmitter comprises at leastfirst and second transmitter circuits each of which processes a signalto be transmitted by a corresponding one of the first and secondantennas. The first transmitter circuit comprises a first upconverterthat upconverts a first in-phase baseband analog signal and a firstquadrature-phase baseband analog signal to generate a first RF frequencysignal; a first bandpass filter coupled to the output of the firstupconverter that filters the first RF frequency signal; and a firstpower amplifier coupled to the output of the first bandpass filter thatamplifies the first filtered RF frequency signal to produce a firstamplified signal that is coupled to the first antenna for transmission.The second transmitter circuit comprises a second upconverter thatupconverts a second in-phase baseband analog signal and a secondquadrature-phase baseband analog signal to generate a second RFfrequency signal; a second bandpass filter coupled to the output of thesecond upconverter that filters the second RF frequency signal; and asecond power amplifier coupled to the output of the second bandpassfilter that amplifies the second filtered RF frequency signal to producea second amplified signal that is coupled to the second antenna fortransmission.

[0079] While the foregoing description has referred to a MIMO radiotransceiver with two antennas, and thus two receiver circuits and twotransmitter circuits, it should be understood that the same conceptsdescribed herein may be extended in general to a radio transceiver withN transmitter circuits and N transmitter circuits for operation with Nantennas.

[0080] The above description is intended by way of example only.

Claims
 1. A multiple-input multiple-output (MIMO) radio transceivercomprising: a. a receiver comprising at least first and second receivercircuits each to process a signal from a corresponding one of first andsecond antennas, i. the first receiver circuit comprising:
 1. a firstdownconverter coupled to the first antenna to downconvert a firstreceive signal detected by the first antenna to produce a first basebandsignal; and
 2. a first lowpass filter coupled to the first downconverterthat lowpass filters the first baseband signal; ii. the second receivercircuit comprising:
 1. a second downconverter coupled to the secondantenna to downconvert a second receive signal detected by the secondantenna to produce a second baseband signal; and
 2. a second lowpassfilter coupled to the second downconverter that lowpass filters thesecond baseband signal; b. a transmitter comprising at least first andsecond transmitter circuits each of which processes a signal to betransmitted by a corresponding one of the first and second antennas, i.the first transmitter circuit comprising:
 1. a first upconverter thatupconverts a first baseband analog signal to generate a first RFfrequency signal;
 2. a first bandpass filter coupled to the output ofthe first upconverter that filters the first RF frequency signal; and 3.a first power amplifier coupled to the output of the bandpass filterthat amplifies the filtered RF frequency signal to produce a firstamplified signal that is coupled to the first antenna for transmission;ii. the second transmitter circuit comprising:
 1. a second upconverterthat upconverts a second baseband analog signal to generate a second RFfrequency signal;
 2. a second bandpass filter coupled to the output ofthe second upconverter that filters the second RF frequency signal; and3. a second power amplifier coupled to the output of the second bandpassfilter that amplifies the second filtered RF frequency signal to producea second amplified signal that is coupled to the second antenna fortransmission.
 2. The radio transceiver of claim 1, wherein the firstreceive signal detected by the first antenna and the second receivesignal detected by the second antenna are components of a single signalto be processed by the radio transceiver, and wherein the first receivercircuit and the second receiver circuit process the first and secondreceive signals substantially simultaneously to allow for combining ofsignals resulting from processing by the first and second receivercircuits.
 3. The radio transceiver of claim 1, wherein the first analogbaseband signal and the second analog baseband signal are weightedcomponents of a single signal, and wherein the first transmitter circuitand the second transmitter circuit process the first and second analogbaseband signals for transmission substantially simultaneously.
 4. Theradio transceiver of claim 1, and further comprising a frequencysynthesizer that produces an RF local oscillator signal that is coupledto each of the first and second downconverters to be mixed with thefirst and second receive signals, respectively, wherein the RF localoscillator signal may be at any frequency within one or more discreteradio frequency bands.
 5. The radio transceiver of claim 4, wherein thefrequency synthesizer couples the RF local oscillator signal to thefirst and second upconverters to up-mix the first and second basebandanalog signals, respectively.
 6. The radio transceiver of claim 1,wherein the first and second receiver circuits and the first and secondtransmitter circuits are implemented on a single semiconductorintegrated circuit.
 7. The radio transceiver of claim 1, wherein thefirst receiver circuit further comprises a first sample-and-hold circuitcoupled to the output of the first lowpass filter and the secondreceiver circuit further comprises a second sample-and-hold circuitcoupled to the output of the second lowpass filter.
 8. The radiotransceiver of claim1, wherein the first and second downconverterscomprise a single stage mixing process to downconvert the first andsecond receive signals directly to baseband.
 9. The radio transceiver ofclaim 8, and further comprising a frequency synthesizer that supplies anRF local oscillator signal to the first and second downconverters,wherein an IF local oscillator signal is derived from the RF localoscillator signal that is also supplied to the first and seconddownconverters.
 10. The radio transceiver of claim 1, wherein the firstand second downconverters comprise a two stage mixing process todownconvert the first and second receive signals to first and secondintermediate frequency signals at a common intermediate frequency, andthen to first and second baseband signals.
 11. The radio transceiver ofclaim 1, wherein the first lowpass filter of the first receiver circuitand the second lowpass filter of the second receiver circuit arevariable lowpass filters that are responsive to a bandwidth controlsignal so as to pass a portion of a radio frequency band orsubstantially the entire radio frequency band.
 12. The radio transceiverof claim 1, wherein the first upconverter and the second upconvertercomprise first and second lowpass filters to filter the first and secondbaseband analog signals, respectively, prior to upconversion, whereinthe first and second lowpass filters are variable lowpass filters thatare responsive to a bandwidth control signal so as to filter the firstand second baseband analog signals for transmission in a portion of theradio frequency band, or in substantially the entire radio frequencyband.
 13. The radio transceiver of claim 1, wherein the firstdownconverter comprises first and second RF mixers, wherein the first RFmixer down-mixes the first receive signal to an intermediate frequencysignal when the first receive signal is in a first radio frequency bandand the second RF mixer down-mixes the first receive signal to anintermediate frequency signal when the first receive signal is in asecond radio frequency band, and wherein the second downconvertercomprises first and second RF mixers, wherein the first RF mixerdown-mixes the second receive signal to an intermediate frequency signalwhen the second receive signal is in a first radio frequency band andthe second RF mixer down-mixes the second receive signal to anintermediate frequency signal when the second receive signal is in thesecond radio frequency band.
 14. A multiple-input multiple-output (MIMO)radio transceiver comprising: a. a receiver comprising at least firstand second receiver circuits each to process a signal from acorresponding one of first and second antennas, i. the first receivercircuit comprising:
 1. a first downconverter coupled to the firstantenna to downconvert a first receive signal detected by the firstantenna to produce a first in-phase baseband signal and a firstquadrature-phase baseband signal; and
 2. first and second lowpassfilters coupled to the first downconverter that lowpass filter the firstin-phase baseband signal and the first quadrature phase baseband signal,respectively; ii. the second receiver circuit comprising:
 1. a seconddownconverter coupled to the second antenna to downconvert a secondreceive signal detected by the second antenna to produce a secondin-phase baseband signal and a second quadrature-phase baseband signal;and
 2. third and fourth lowpass filters coupled to the seconddownconverter that lowpass filter the second in-phase baseband signaland the second quadrature-phase baseband signal; b. a transmittercomprising at least first and second transmitter circuits each of whichprocesses a signal to be transmitted by a corresponding one of the firstand second antennas, i. the first transmitter circuit comprising:
 1. afirst upconverter that upconverts a first in-phase baseband analogsignal and a first quadrature-phase baseband analog signal to generate afirst RF frequency signal;
 2. a first bandpass filter coupled to theoutput of the first upconverter that filters the first RF frequencysignal; and
 3. a first power amplifier coupled to the output of thefirst bandpass filter that amplifies the first filtered RF frequencysignal to produce a first amplified signal that is coupled to the firstantenna for transmission; ii. the second transmitter circuitcomprising:
 1. a second upconverter that upconverts a second in-phasebaseband analog signal and a second quadrature-phase baseband analogsignal to generate a second RF frequency signal;
 2. a second bandpassfilter coupled to the output of the second upconverter that filters thesecond RF frequency signal; and
 3. a second power amplifier coupled tothe output of the second bandpass filter that amplifies the secondfiltered RF frequency signal to produce a second amplified signal thatis coupled to the second antenna for transmission.
 15. The radiotransceiver of claim 14, wherein the first downconverter comprises firstand second RF mixers, wherein the first RF mixer down-mixes the firstreceive signal to an intermediate frequency signal when the firstreceive signal is in a first radio frequency band and the second RFmixer down-mixes the first receive signal to an intermediate frequencysignal when the first receive signal is in a second radio frequencyband, and wherein the second downconverter comprises first and second RFmixers, wherein the first RF mixer down-mixes the second receive signalto an intermediate frequency signal when the second receive signal is ina first radio frequency band and the second RF mixer down-mixes thesecond receive signal to an intermediate frequency signal when thesecond receive signal is in the second radio frequency band.
 16. Theradio transceiver of claim 15, wherein the first downconverter furthercomprises a pair of quad mixers coupled to the output of the first andsecond RF mixers to further down-mix the intermediate frequency signalto the first in-phase and quadrature baseband signals representative ofthe first receive signal, and the second downconverter further comprisesa pair of quad mixers coupled to the output of the first and second RFmixers to further down-mix the intermediate frequency signal to thesecond in-phase and quadrature baseband signals representative of thesecond receive signal.
 17. The radio transceiver of claim 16, andfurther comprising an RF frequency synthesizer that generates an RFlocal oscillator signal for the RF mixers in the first and seconddownconverters and wherein an intermediate frequency local oscillatorsignal used by the quad mixers in the first and second downconverters isderived from the RF mixing signal.
 18. The radio transceiver of claim17, and further comprising a divide-by-four circuit coupled to the RFfrequency synthesizer that divides the frequency of the RF localoscillator signal to generate the intermediate frequency localoscillator signal that is coupled to the quad mixers in the first andsecond downconverters.
 19. The radio transceiver of claim 16, andfurther comprising an RF frequency synthesizer that generates an RFlocal oscillator signal for the RF mixers and an intermediate frequencysynthesizer that generates an intermediate frequency local oscillatorsignal for the quad mixers in the first and second downconverters. 20.The radio transceiver of claim 14, wherein the first downconvertercomprises a pair of quad mixers that down-mix the first receive signaldirectly to the first in-phase and quadrature baseband signals, and thesecond downconverter comprises a pair of quad mixers that down-mix thesecond receive signal directly to the second in-phase and quadraturebaseband signals.
 21. The radio transceiver of claim 20, wherein thefirst and second receiver circuits each further comprise a variableamplifier coupled to amplify the intermediate frequency signal before itis supplied to their quad mixers.
 22. The radio transceiver of claim 14,wherein the first upconverter comprises a pair of quad mixers thatup-mix the first baseband in-phase and quadrature signals to anintermediate frequency signal, the second upconverter comprises a pairof quad mixers that up-mix the second baseband in-phase and quadraturesignals to an intermediate frequency signal.
 23. The radio transceiverof claim 21, wherein the first upconverter further comprises an RF mixercoupled to the output of the quad mixers that up-mixes the intermediatefrequency signal to a first RF signal, and the second upconverterfurther comprises an RF mixer coupled to the output of the quad mixersthat up-mixes the intermediate frequency signal to a second RF signal.24. The radio transceiver of claim 23, wherein the first and secondtransmitter circuits each further comprises a variable amplifier coupledto amplify the intermediate frequency signal before it is supplied totheir RF mixers.
 25. The radio transceiver of claim 23, wherein thefirst and second transmitter circuits further comprise first and secondbandpass filters coupled to the output of their RF mixers, that arededicated to bandpass filtering signals to be transmitted in a firstradio frequency band, and third and fourth bandpass filters coupled tothe RF mixers to filter signals to be transmitted in a second radiofrequency band.
 26. The radio transceiver of claim 14, wherein the firstreceiver circuit comprises first and second sample-and-hold circuitsthat are connected to the first and second lowpass filters,respectively, to couple the first in-phase baseband signal and the firstquadrature-phase baseband signal to an analog-to-digital converter, andthe second receiver circuit comprises third and fourth sample-and-holdcircuits that are connected to the third and fourth lowpass filters,respectively, to couple the second in-phase baseband signal and thesecond quadrature-phase baseband signal to an analog-to-digitalconverter.
 27. The radio transceiver of claim 14, wherein the receiverand the transmitter are implemented on a single semiconductor integratedcircuit.
 28. The radio transceiver of claim 14, wherein the firstreceive signal detected by the first antenna and the second receivesignal detected by the second antenna are components of a single signalto be processed by the radio transceiver, and wherein the first receivercircuit and the second receiver circuit process the first and secondsignals substantially simultaneously to allow for combining of signalsresulting from processing by the first and second receiver circuits. 29.The radio transceiver of claim 14, wherein the first analog basebandsignal and the second analog baseband signal are weighted components ofa single signal, and wherein the first transmitter circuit and thesecond transmitter circuit process the first and second analog basebandsignals for transmission substantially simultaneously.
 30. The radiotransceiver of claim 14, wherein the first, second, third and fourthlowpass filters are variable lowpass filters that are responsive to abandwidth control signal so as to pass a portion of a radio frequencyband or to pass substantially the entire radio frequency band.
 31. Theradio transceiver of claim 30, wherein the first and second variablelowpass filters receive as input the first in-phase baseband analogsignal and the first quadrature phase baseband analog signal,respectively, and the third and fourth lowpass filters receive as inputthe second in-phase baseband analog signal and the secondquadrature-phase baseband analog signal, respectively, to filter thesesignals for transmission in a portion of the radio frequency band, or insubstantially the entire radio frequency band.
 32. The radio transceiverof claim 14, wherein the first transmitter circuit comprises first andsecond variable lowpass filters to filter the first in-phase andquadrature-phase signals prior to upconversion and the secondtransmitter circuit comprises third and fourth variable lowpass filtersto filter the second in-phase and quadrature-phase signals prior toupconversion, wherein the first, second, third and fourth variablelowpass filters in the first and second transmitter circuits arevariable lowpass filters that are responsive to a bandwidth controlsignal so as to filter the first and second baseband analog signals fortransmission in a portion of the radio frequency band, or insubstantially the entire radio frequency band.
 33. The radio transceiverof claim 14, wherein the first downconverter and the seconddownconverter downconvert the first and second receive signals,respectively, directly to baseband in a single stage downconversionprocess.
 34. In combination, the radio transceiver of claim 14, andfurther comprising: a. an analog-to-digital converter (ADC); b. adigital-to-analog converter (DAC); and c. a digital multiplexer coupledto the ADC and to the DAC; d. wherein the ADC receives as input one of:an analog transmit power level signal, first or second quadraturebaseband analog signal, first or second in-phase baseband analog signal;and wherein the DAC receives as input one of: first or second digitalquadrature-phase transmit signal, first or second digital in-phasetransmit signal, digital receiver gain control signal, and wherein thedigital multiplexer directs signals from the ADC to their appropriatedestination and directs appropriate ones of the signals to the DAC fordigital-to-analog conversion.
 35. The combination of claim 34, andfurther comprising a first switch having first and second inputterminals and an output terminal, the output terminal of the firstswitch being coupled to the input of the ADC, the first and inputterminals of the first switch being coupled to any two signals of: theanalog transmit power level signal, first or second quadrature basebandanalog signal, and the first or second in-phase baseband analog signal,and a second switch having first and second output terminals and aninput terminal, the input terminal of the second switch being coupled tothe output of the DAC, and wherein the digital multiplexer directs oneof the following signals to the input of the DAC: the first or seconddigital quadrature-phase transmit signal, first or second digitalin-phase transmit signal, and the digital receiver gain control signal.36. In combination, the radio transceiver of claim 14, and a front-endsection comprising: a. a first transmit/receive switch to be coupled tothe first antenna and a second transmit/receive switch to be coupled tothe second antenna, wherein the first and second transmit/receiveswitches each comprise an antenna terminal to be coupled to the firstand second antenna, respectively, a receive output terminal and atransmit input terminal, the transmit input terminals of the first andsecond transmit/receive switches being coupled to the output of thefirst and second transmitter circuits, respectively, wherein the firstand second transmit/receive switches are responsive to a control signalto select one of the two output terminals; and b. first and secondbandpass filters, the first bandpass filter coupled to the receiveoutput terminal of the first transmit/receive switch and the secondbandpass filter coupled to the receive output terminal of the secondtransmit/receive switch, the first and second bandpass filters filterthe signals detected by the first and second antennas, respectively, toproduce the first and second receive signals.
 37. The combination ofclaim 36, wherein the first and second bandpass filters are dedicated tofiltering signals in a first radio frequency band, and furthercomprising: a. third and fourth bandpass filters dedicated to filteringsignals in a second radio frequency band; b. first and second bandselect switches, the first and second band selection switches having aninput terminal coupled to the receive output terminals of the first andsecond transmit/receive switches, respectively, and each having a firstoutput terminal coupled to the first and second bandpass filters,respectively, and a second output terminal coupled to the third andfourth bandpass filters, respectively.
 38. The combination of claim 37,wherein the radio front-end section further comprises third and fourthband select switches, each having first and second input terminals, andan output terminal, the output terminal of the third and fourth bandselect switches being coupled to the transmit input terminals of thefirst and second transmit/receive switches.
 39. The combination of claim38, wherein the radio front-end section further comprises first andsecond lowpass filters dedicated to filtering signals to be transmittedin the first radio frequency band, the outputs of the first and secondlowpass filters being connected to the first input terminals of thethird and fourth band select switches, respectively, and third andfourth lowpass filters dedicated to filtering signals to be transmittedin the second radio frequency band, the outputs of the third and fourthlowpass filters being connected to the second input terminals of thethird and fourth band select switches.
 40. In combination, the radiotransceiver of claim 14, and a radio front-end section, wherein theradio-front end section comprises a first diplexer to be coupled to thefirst antenna and a second diplexer to be coupled to the second antenna,wherein the first and second diplexers each have first and secondbranches onto which signals from first and second radio frequency bands,respectively, are coupled for transmission via the first and secondantennas, respectively, or are coupled when received by the first andsecond antennas, respectively.
 41. The combination of claim 40, whereinfor each diplexer, the radio front-end section further comprises abandpass filter coupled in the first branch to filter signals receivedin the first frequency band and a bandpass filter coupled in the secondbranch to filter signals received in the second frequency band.
 42. Thecombination of claim 41, wherein the radio-front end section furthercomprises a transmit/receive switch coupled to the bandpass filter ineach of the first and second branches for each diplexer, wherein thetransmit/receive switch selects either a signal to be transmittedthrough an antenna coupled to the associated diplexer, or a signaldetected by an antenna coupled to the associated diplexer which iscoupled to the bandpass filter for that branch.
 43. The combination ofclaim 41, wherein the radio transceiver further comprises atransmit/receive switch coupled to the bandpass filter in each of thefirst and second branches for each diplexer, wherein thetransmit/receive switch selects either a signal to be transmittedthrough an antenna coupled to the associated diplexer, or a signaldetected by an antenna coupled to the associated diplexer which iscoupled to the bandpass filter for that branch.
 44. The combination ofclaim 43, wherein the radio front-end section further comprises aquarter wavelength element coupled between the transmit/receive switchand the bandpass filter in each of the first and second branches foreach diplexer.
 45. A multiple-input multiple-output (MIMO) radiotransceiver on a single semiconductor integrated circuit, comprising: a.a receiver comprising at least first and second receiver circuits eachto process a signal from a corresponding one of first and secondantennas, i. the first receiver circuit comprising:
 1. a firstdownconverter coupled to the first antenna to downconvert a firstreceive signal detected by the first antenna to produce a first basebandsignal; and
 2. a first lowpass filter coupled to the first downconverterthat lowpass filters the first baseband signal; ii. the second receivercircuit comprising:
 1. a second downconverter coupled to the secondantenna to downconvert a second receive signal detected by the secondantenna to produce a second baseband signal; and
 2. a second lowpassfilter coupled to the second downconverter that lowpass filters thesecond baseband signal; b. a transmitter comprising at least first andsecond transmitter circuits each of which processes a signal to betransmitted by a corresponding one of the first and second antennas, i.the first transmitter circuit comprising:
 1. a first upconverter thatupconverts a first baseband analog signal to generate a first RFfrequency signal; and
 2. a first bandpass filter coupled to the outputof the first upconverter that filters the first RF frequency signal; ii.the second transmitter circuit comprising:
 1. a second upconverter thatupconverts a second baseband analog signal to generate a second RFfrequency signal; and
 2. a second bandpass filter coupled to the outputof the second upconverter that filters the second RF frequency signal.46. The radio transceiver of claim 45, wherein the first receive signaldetected by the first antenna and the second receive signal detected bythe second antenna are components of a single signal to be processed bythe radio transceiver, and wherein the first receiver circuit and thesecond receiver circuit process the first and second receive signalssubstantially simultaneously to allow for combining of signals resultingfrom processing by the first and second receiver circuits.
 47. The radiotransceiver of claim 45, wherein the first analog baseband signal andthe second analog baseband signal are weighted components of a singlesignal, and wherein the first transmitter circuit and the secondtransmitter circuit process the first and second analog baseband signalsfor transmission substantially simultaneously.
 48. The radio transceiverof claim 45, and further comprising a frequency synthesizer thatproduces an RF local oscillator signal that is coupled to each of thefirst and second downconverters to be mixed with the first and secondreceive signals, respectively, wherein the RF local oscillator signalmay be at any frequency within one or more discrete radio frequencybands.
 49. The radio transceiver of claim 48, wherein the frequencysynthesizer couples the RF local oscillator signal to the first andsecond upconverters to upmix the first and second baseband analogsignals, respectively.
 50. The radio transceiver of claim 45, whereinthe first and second downconverters comprise a single stage mixingprocess to downconvert the first and second receive signals directly tobaseband.
 51. The radio transceiver of claim 50, wherein the firstdownconverter comprises a pair of quad mixers that down-mix the firstreceive signal directly to first in-phase and quadrature basebandsignals, and the second downconverter comprises a pair of quad mixersthat down-mix the second receive signal directly to the second in-phaseand quadrature baseband signals.
 52. The radio transceiver of claim 45,wherein the first lowpass filter of the first receiver circuit and thesecond lowpass filter of the second receiver circuit are variablelowpass filters that are responsive to a bandwidth control signal so asto pass a portion of a radio frequency band or substantially the entireradio frequency band.
 53. The radio transceiver of claim 45, wherein thefirst upconverter and the second upconverter comprise first and secondlowpass filters to filter the first and second baseband analog signals,respectively, prior to upconversion, wherein the first and secondlowpass filters are variable lowpass filters that are responsive to abandwidth control signal so as to filter the first and second basebandanalog signals for transmission in a portion of the radio frequencyband, or in substantially the entire radio frequency band.